The present invention relates generally to charge coupled devices (CCD's) with registers, such as CCD delay lines, for transferring electrical charges. More particularly, the invention relates to an input structure for CCD's capable of automatic adjustment of DC input bias charge.
Recently, CCD delay lines have come to be widely used in television sets and the like for delay processing. When employed in television sets, CCD delay lines are used for delay processing of analog signals, such as video signals. A DC input bias charge is commonly applied to an input section to which input signals for the CCD delay line are applied.
In the prior art, this input bias is provided by an external amplitude control of some sort. The external control is adjusted to apply a bias charge at a predetermined level to the input section of the CCD. In this conventional structure, the input bias level tends to fluctuate due to variations in the temperature-dependent characteristics of the input section. In addition, difficulty has been encountered in accurately adjusting the input bias charge by means of the external amplitude control.
For example, U.S. Pat. No. 4,139,784 discloses an CCD input circuit capable of adjusting the DC input bias to a CCD signal register serving as a CCD delay line. Feedback control of the DC input bias is performed by comparing the electric charge transferred through a reference register with a constant reference signal from a reference voltage source. However, the difficulty mentioned above may be encountered even with this structure since adjustment of the reference voltage from the reference voltage source would still be necessary. Furthermore, it may be difficult to adjust the reference voltage in precise correspondence to variations in the properties of the reference register due to the influence of temperature variations and so forth.